1. Field of the Invention
The invention relates generally to the field of photography, and more particularly to a frame or exposure counter for a camera.
2. Description of the Prior Art
Typically in many known 35 mm cameras, there is included a motorized film transport mechanism. In operation, a leading end portion of the filmstrip extending from a light-tight cartridge loaded in the camers is attached automatically to a take-up spool. The take-up spool is rotated after each exposure to advance successive frames of the filmstrip from the cartridge across the focal plane of a taking lens and onto the take-up spool. Each time the take-up spool is rotated, a single unexposed frame of the filmstrip is located in the focal plane of the taking lens and a preceding exposed frame is wound onto the take-up spool. At the same time, a frame or exposure counter is incremented by rotation of a metering sprocket in engagement with successive perforations in the filmstrip to provide a count of the number of frames exposed or remaining to be exposed on the filmstrip.
FIGS. 1-4 of the accompanying drawings are a detailed representation of a prior art exposure counter in a 35 mm camera. Usually the metering sprocket, now shown, and a metering gear 1 are coaxially coupled to allow the two to rotate in unison. The metering gear 1 continuously engages an intermediate gear 3 which in turn continuously engages a drive gear 5. A cylindrical drive member 7 is coaxially fixed atop the drive gear 5 and has a single v-shaped recess 9 for receiving respective peripheral teeth 11 of a rotatable counter disk 13, to rotate the disk in accordance with rotation of the metering sprocket as the filmstrip is advanced by the motorized transport as the filmstrip is advanced by the motorized transport mechanism. The counter disk 13 has thirty-six evenly spaced numerical settings designated by the numbers "1, 2, 3, 4, 5 . . . 36" imprinted on the disk at corresponding locations, a starting or preliminary setting designated by the letter "S" imprinted on the disk at a location preceding the number "1", and two similarly spaced intermediate settings designated by respective dots ". . " imprinted on the disk at corresponding locations between the "S" and the "1". Each of these settings is separated from the next one by a space equivalent to slightly more than the width of the respective frames of the filmstrip. Thus, when visible in a window 15 of the camera, the numbers "1-36" indicate successive frames, the letter "S" usually indicates that the camera is empty, and the dots " . . " indicate that a leader section of the filmstrip is being advanced onto the take-up spool.
When a rear door 17 of the camera is opened as shown in FIG. 2, a separating spring 19 urges a swing arm 21 to pivot counter-clockwise about a shaft 23 for the intermediate gear 3. This causes the drive member 7 to move out of its position for engaging one of the peripheral teeth 11 of the counter disk 13. If the counter disk 13 is at a setting other than its starting setting "S" as shown in FIG. 1, an initializing spring 25 will urge the disk to rotate counter-clockwise to initialize the disk to the starting setting. A stop pin 27 secured to the underside of the counter disk 13 is disposed to contact a fixed pin 29 to halt the disk at its starting setting "S" as shown in FIG. 2.
When the rear door 17 is re-closed, it pivots the swing arm 21 clockwise about the shaft 23 to return the drive member 7 to a position within a gap 31 between a first one 11a of the peripheral teeth 11 of the counter disk 13 and a last one 11z of the teeth as shown in FIG. 3. If a film cartridge has been loaded in the camera and the motorized transport mechanism is energized, the leader section of the filmstrip will be advanced onto the take-up spool and a first frame will be positioned for exposure. Each time the filmstrip is advanced slightly more than the width of a single frame, the metering sprocket is rotated a single completion revolution, i.e. 360.degree.. This will cause the drive member 7 to be similarly rotated in engagement with one of the teeth 11 of the counter disk 13, to rotate the disk the equivalent of one frame to its next setting. A metering switch, now shown, is normally opened each time the metering sprocket is rotated a complete revolution, to de-energize the motorized transport mechanism and thereby halt film advance. However, since the leader section of the filmstrip has a length equal approximately to three times the width of a single frame, a means must be provided for defeating the metering switch temporarily to allow the film leader to be wound without interruption onto the take-up spool in order to position a first frame for exposure. Specifically, as shown in FIGS. 1 and 2, the means comprises an override switch 33 which, when closed, nullifies the metering switch. In operation, after the counter disk 13 is rotated from its startng setting "S" and almost to its first intermediate setting ".", a cam rise 35 on a camming disk 37 coaxially fixed to the counter disk closes the override switch 33. The override switch 33 remains closed until a cam descent 39 on the camming disk 37 is rotated alongside the switch. This is timed to concur with rotation of the counter disk 13 to its second intermediate setting ".". Then, after the metering sprocket is rotated another revolution to coincide with advance of the filmstrip to position the first frame for exposure, the metering switch is re-opened to de-energize the motorized transport mechanism. Simultaneously, the counter disk 13 is indexed to its first numbered setting "1".
When the drive member 7 is rotated from a starting angular position, within a gap 31, adjacent the first tooth 11a of the counter disk 13 as shown in FIG. 3, it may or may not be rotated a complete revolution, i.e. 360.degree., at the conclusion of its first revolution. The reason for the drive member 7 being rotated less than a complete revolution is that they may be some lost motion due to gear backlash or other causes, when the motorized transport mechanism is first actuated following a previous reverse movement of the transport mechanism to rewind an exposed film back into the cartridge. If the drive member 7 is rotated a complete revolution, the counter disk 7 will be rotated sufficiently to temporarily close the override switch 33. That is, the counter disk 7 will be rotated from its starting setting "S" to its first intermediate setting ".". Conversely, if the drive member 7 is rotated less than a complete revolution, then, depending upon the starting angular position of the drive member, the counter disk 7 may or may not be rotated sufficiently to temporarily close the override switch 33. When the drive member 7 is in the starting angular position shown in FIG. 3, and it is rotated less than a complete revolution from that position, the drive member will engage the first tooth 11a of the counter disk 13 shortly after it is actuated. Consequently, the counter disk 13 will be rotated sufficiently to close the override switch 33. However, when the drive member 7 is in the starting angular position shown in FIG. 4, and it is rotated less than a complete revolution from that position (as indicated by the reference number 7' in FIG. 4), the drive member will not engage the first tooth 11a of the counter disk 13 until shortly before the end of its cycle. Consequently, the counter disk 13 will not be rotated sufficiently (as indicated by the reference number 11a' in FIG. 4) to close the override switch 33. In this instance, therefore, the override switch 33 will not nullify the metering switch and the motorized transport mechanism will be de-energized prematurely, before the first frame is positioned for exposure.